McLaren-Honda's troubled pre-season continued on Thursday as the second winter test at Barcelona began.
At lunch on day one at the Circuit de Catalunya, Jenson Button's work at the wheel of the MP4-...

McLaren-Honda's troubled pre-season continued on Thursday as the second winter test at Barcelona began.

At lunch on day one at the Circuit de Catalunya, Jenson Button's work at the wheel of the MP4-30 was over when a design fault on the 'MGU-K' component of the Honda power unit's energy recovery system was found.

McLaren confirmed that the faulty seal causes the "full replacement of the power unit".

And similar problems may strike on Friday, when Fernando Alonso is due to take the wheel.

Honda chief Yasuhisa Arai confirmed that the part has to be re-designed, but until that is complete "we may face the same problem when we run again tomorrow".

McLaren added on Twitter: "Such issues are all part of testing and we will plan for a productive day of running with Fernando behind the wheel tomorrow."